Mania et al. 2020 — Nickel in cereal grains and grain-based products, Poland
This peer-reviewed study from Poland’s National Institute of Public Health measured nickel content in 56 samples of cereal grains and grain-based products purchased from the Polish market in 2019–2020, using GFAAS (graphite furnace atomic absorption spectrometry) after microwave acid digestion, and assessed dietary exposure relative to EFSA’s 2020 tolerable daily intake (TDI) of 13 µg Ni/kg bw/day. Mean (middle-bound) nickel across all 56 samples was 0.66 mg/kg, with a 95th percentile of 1.93 mg/kg; whole grains contained higher concentrations (mean 1.16 mg/kg) than processed grain products (mean 0.61 mg/kg). Estimated exposures for adults and children from cereal grains and products ranged from 1.1% to 13.4% of the EFSA TDI, with no health concern identified at population level, though individual sample contamination reached 4.80 mg/kg in millet and 2.53 mg/kg in oat flakes. No EU maximum level for nickel in food existed at the time of the study; only drinking water and food additives had EU-level Ni requirements.
Key numbers
All concentrations in mg/kg (= ppm) fresh weight; middle-bound (MB) treatment of left-censored data (27% of results below LOQ of 0.06 mg/kg):
| Category | n | Mean (MB) mg/kg | P95 (MB) mg/kg | SD (MB) |
|---|---|---|---|---|
| Cereal grains (millet, rye, wheat, barley) | 5 | 1.16 | 3.91 | 2.04 |
| Pasta | 11 | 0.26 | 1.04 | 0.52 |
| Flour | 13 | 0.35 | 1.35 | 0.58 |
| Groats | 12 | 0.63 | 1.72 | 0.67 |
| Flakes | 10 | 0.93 | 1.97 | 0.66 |
| Bran | 5 | 1.34 | 1.76 | 0.36 |
| All grain-based products | 51 | 0.61 | 1.84 | 0.66 |
| Cereal grains and grain-based products (all) | 56 | 0.66 | 1.93 | 0.85 |
Individual highlights:
- Millet (grain): range not fully reported individually; overall grain max 4.80 mg/kg
- Rye (grain): 0.10 mg/kg (lowest grain value)
- Roasted buckwheat groat: 1.81 mg/kg (highest reported groat value)
- Oat flakes: 2.53 mg/kg (highest reported flake value; highest single product value in study)
- Whole wheat flour: 0.23–2.12 mg/kg
- Wheat flour (refined): below LOQ
- Spelt flour: 0.14–0.18 mg/kg
- Whole grain pasta: 0.20–1.79 mg/kg
- Regular wheat pasta: 0.03–0.08 mg/kg
Comparative EU context (EFSA 2020 occurrence data cited): Mean (LB-UB) for grains and grain-based products: 0.31–0.33 mg/kg; P95: 1.25 mg/kg. This study’s values are modestly higher.
Exposure estimates as % of EFSA TDI (13 µg Ni/kg bw/day):
- Adults (WHO GEMS/Food cereal grain consumption, excluding rice): 13.4% TDI
- Adults (average cereal product consumption, excluding bread/rice/bakery): 1.1% TDI; children: 3.9% TDI
- At P95 contamination: 3.4% TDI (adults), 11.8% TDI (children)
- Pasta only: below 0.5% TDI (adults), 1.3% TDI (children)
Method parameters: GFAAS (VARIAN SpectrAA 880Z), microwave mineralization with HNO3/H2O2; LOD 0.95 µg/L; LOQ 1.25 µg/L (in-solution) = 0.06 mg/kg in food; recovery 97%; RSDr 7%; validated against NIST SRM 1515 Apple Leaves.
Methods (brief)
Analytical method: GFAAS with Zeeman background correction after microwave closed-vessel acid digestion (0.5 g sample, HNO3 + H2O2). LOQ in food matrix: 0.06 mg/kg. 27% of results below LOQ; EFSA’s substitution method applied (LB=0, MB=LOQ/2, UB=LOQ). External validation via FAPAS and EURL-MN proficiency testing. Nickel only — no other metals measured.
Implications
Certification: This is the most methodologically rigorous nickel-in-cereals study encountered in this batch. GFAAS is appropriate for Ni quantification and the study uses an accredited, EFSA-validated treatment of left-censored data. The finding that bran, whole-grain flakes (especially oats), and whole-grain flour carry 3–6x higher Ni than refined flour or pasta is directly relevant to ingredient sourcing decisions for products targeting nickel-sensitive consumers. EFSA identified grains as contributing up to 49% of infant/toddler dietary Ni exposure; this study’s data supports that conclusion.
Courses: Illustrates the whole-grain vs. refined-grain Ni gradient clearly. The EFSA TDI progression (2.8 µg/kg bw/day in 2015 → 13 µg/kg bw/day in 2020) is a useful teaching example of how risk assessments evolve. The absence of an EU maximum level for Ni in food (only drinking water and additives regulated) is a current regulatory gap worth noting.
App: Mean (MB) values by category are usable as region-specific estimates for Polish/EU market products. The oat flakes P95 of 1.97 mg/kg (1,970 ppb) and bran P95 of 1.76 mg/kg (1,760 ppb) are the most relevant inputs for high-bran and high-oat ingredients. Unit conversion: 0.66 mg/kg = 660 µg/kg = 660 ppb (Ni); 1.93 mg/kg (P95) = 1,930 ppb.